The present invention regards a sand handling system and a method for handling sand.
Sand through rotating equipment should generally be avoided as it reduces the performance of the equipment and will in many cases cause early failure. This issue can be solved by selecting more robust materials for the pump internals but it only prolongs the pump runlife for a limited period of time. Hence, if sand can be prevented from entering the pump it will have a significant impact on pump runlife.
In onshore applications one may separate the sand from a production stream and relatively easily handle the sand. In subsea applications the handling of sand separated out from a well stream is not easy. One may not discharge the sand to the surroundings as this would lead to pollution, which should be avoided. The sand must be handled. There are several earlier proposals for the removal of sand in a well stream. In one proposal the sand is accumulated in the separation tank and periodically flushed from tank downstream of the pump. Such a solution would affect the well stream in periods, giving periods with large quantities of sand and other periods with small quantities of sand, which is not desirable. In another proposal a retrievable sand tank is used. This is designed to be retrieved to the surface when full. Retrieving the sand tank, however, is becoming more difficult as the water depths are increasing.
WO 2004/003335 A1 discloses an underwater system having a hydro-cyclone for separating sand from seawater, and a pump downstream from the hydro-cyclone for drawing seawater upstream of the hydro-cyclone into the hydro-cyclone. The sand separated from the seawater is collected in a sand storage device below the hydro-cyclone. The pump pumps the seawater from which the sand has been removed into a water injection well and a portion of the seawater is diverted into a sand extraction device beneath the sand storage device to flush away the sand collected therein.
WO 03/041838 A1 is concerned with a method and apparatus for collecting and then disposing of sand contained in production fluid where the production mixture is directed through a sand removal unit having a retrievable module installed in a modular seabed processing system, in which the unit collects sand from the mixture. The production fluid mixture then enters a fluid separation chamber in the module, where it is separated into a gas and a mixture of oil and water. Seawater is drawn in from outside the module and is pumped into the sand removal unit to flush the collected sand. The mixed flushed sand and seawater is commingled with the mixture of oil and water downstream of the fluid separation chamber and the commingled mixture is conveyed to a host facility. There, the sand is separated from the commingled mixture and disposed of.
C. H. Rawlins, Kvaerner Process Systems; S. E. Staten, Chevron USA Production Company; I. I. Wang, Kvaerner Process Systems: “Design and Installation of a Sand Separation and Handling System for a Gulf of Mexico Oil Production Facility”, Society of Petroleum Engineers, and GB 2 342 057 A are also concerned with the separation of sand from a well stream.
An aim with the present invention is to provide a subsea sand handling system which alleviates some of the problems associated with the known systems. This is achieved with a system and method as defined in the attached claims.